1. Background
This invention relates generally to suspension systems of high performance motor vehicles. More specifically but not by way of limitation, the present invention relates to a traction device for limiting wrap-up of a leaf spring during acceleration of a motor vehicle.
2. Discussion
Conventional leaf springs are widely used in rear-wheel drive vehicles. During acceleration, the leaf spring is subject to twisting forces which are opposite in direction to the acceleration of the drive wheels. The opposed twisting forces are commonly referred to as “wrap-up” and often contributes to rear wheel “hop”.
In an effort to minimize leaf spring wrap-up and rear wheel “hop” on acceleration, a number of devices have been designed to minimize leaf spring wrap-up and rear-wheel hop during acceleration. One of these is a simple bolt-on traction bar. A rigid bar, generally of steel, has a mounting pad on one end for attachment to the point at which the rear axle meets the leaf spring assembly. A rubber “snubber” at the other end is used to attach the rigid bar to the front eye of the leaf spring. The length of the bar extends forward from the mounting pad to a point under the front leaf spring eye. During acceleration, the counter-rotation of the rear axle is arrested when the snubber meets the spring eye.
Bolt-on traction bars decrease leaf spring wrap-up, help to prevent rearwheel hop, and aid in improving rear wheel traction during acceleration. Additionally, the bolt-on traction bars are typically relatively inexpensive and easy to install.
Several other devices have been devised which represent improvements over the bolt-on traction bar. One such device is the ladder bar and another is the 4-link system. The ladder bar device comprises two mounting assemblies. One end of each mounting assembly is welded to the rear axle housing and the other is welded to a forward point of the chassis. These mounting assemblies are interconnected by a tubing structure. The 4-link system, which sometimes eliminates the conventional leaf spring from the motor vehicle, utilizes two 2-link assemblies (one on each side). One end of each 2-link assembly is welded to the rear axle housing and the other end is welded to a forward location on the chassis. Adjustable tubular links connect the rear axle housing to the chassis.
Each of these improved devices reduces leaf spring wrap-up and rear wheel hop, improves traction, and adjusts the instant center (the point at which the rear wheels push the vehicle forward). The ladder bar and the 4-link system, which are more expensive than simple bolt-on traction bars, require professional installation.
In U.S. Pat. No. 5,354,092 (Calvert), an improved traction bar includes a rear support assembly attached to the rear axle and the leaf spring and a front support assembly pivotally attached to the front end of the leaf spring. A rigid link extends between the rear support assembly and the front support assembly. The front support assembly is attached to the front of the leaf spring by a bushing which extends through the eye of leaf spring. The front support assembly includes a pivot stop which engages the upper surface of the leaf spring and limits movement of the front support assembly relative to the front end of the leaf spring. The pivotal movement limiting means includes means for engaging an upper surface of the leaf spring in the form of a pivot stop which extends across the upper surface of the leaf spring. The front support assembly includes a pair of generally triangular pivot plates which are pivotally attached to the front end of the leaf spring. The triangular pivot plates support the pivot stop at a fixed distance from the front end of the leaf spring and provide a point of attachment for the rigid link below the front end of the leaf spring. The pivot plates are secured to one another by three bolts positioned generally adjacent to the three corners of the triangular plates. The bolts serve to provide a pivot axis for the front support assembly relative to the front end of the leaf spring, the pivot stop itself, and the location of the point of attachment of the rigid link to the front support assembly. The rigid link is adjustable in length through the use of a threaded front eye connector and an oppositely threaded rear eye connector. Rotation of the rigid link thus changes the overall length of the rigid link.
While providing some improvement in leaf spring wrap-up, rear wheel hop, traction, and movement of the instant center forward with respect to the rear axle, the Calvert patent's effectiveness is limited by the structure of the front support assembly. The use of triangular pivot plates restrict the location of the pivot stop on the top surface of the leaf spring to a position comparatively close to the front eye of the leaf spring. Optional mounting apertures in the triangular pivot plates permit limited optional location of the threaded front eye connector of the rigid link, but additional adjustability is always helpful.
Accordingly, a need remains for a traction device for motor vehicles which is more effective in preventing leaf spring wrap-up and rear wheel hop by moving the vehicle instant center forward with respect to the rear axle and, simultaneously, improving traction during hard acceleration.